There are many types of data storage systems available today. Some of these systems store data cartridges (e.g., DLT cartridges) at known locations, and retrieve desired data cartridges from the known locations so that data may be written to or read from the data cartridges. Such data storage systems are often referred to as “cartridge libraries”, particularly if they can accommodate a large number of data cartridges.
A typical cartridge library may include one or more different types of cartridge-receiving devices for holding the library's various data cartridges. One type of cartridge-receiving device may comprise a cartridge storage rack, while another type of cartridge-receiving device may comprise a cartridge read/write device or “drive”. The cartridge storage racks serve to provide storage locations for data cartridges that are not currently in use. Often, a cartridge storage rack will be designed to hold a number of cartridge magazines, with each magazine holding a predetermined subset of data cartridges. In this manner, it is easier to add and/or remove data cartridges from a cartridge library.
A cartridge library may also be provided with a movable cartridge-engaging assembly or “picker” for transporting data cartridges between a library's various cartridge-receiving devices (e.g., between cartridge storage racks and cartridge drives). A typical cartridge-engaging assembly may also be provided with a plunge mechanism or “thumb assembly” for engaging the various data cartridges contained in the cartridge-receiving devices and drawing them into the cartridge-engaging assembly. A positioning system associated with the cartridge-engaging assembly may be used to move the cartridge-engaging assembly between the various cartridge-receiving devices.
Cartridge libraries of the type described above are usually connected to a host computer system that reads and writes the data cartridges. For example, if the host computer system issues a request for data contained on a particular data cartridge, a control system associated with the cartridge library will actuate the positioning system to move the cartridge-engaging assembly along the cartridge storage racks until the cartridge-engaging assembly is positioned adjacent a desired data cartridge. The plunge mechanism associated with the cartridge-engaging assembly may then extend, engage the data cartridge, remove the data cartridge from its cartridge storage rack, and then retract to draw the data cartridge into the cartridge-engaging assembly. Thereafter, the positioning system may be actuated to move the cartridge-engaging assembly to an appropriate cartridge drive. Once properly positioned adjacent the cartridge drive, the plunge mechanism may extend to insert the selected data cartridge into the cartridge drive so that the host computer may thereafter read and/or write the data cartridge. After the read/write operation is complete, the plunge mechanism may be actuated to remove the data cartridge from the cartridge drive, and the cartridge-engaging assembly may be actuated to return the data cartridge to its cartridge storage rack.
A cartridge library encompassing many of the above features is disclosed in U.S. Pat. No. 6,025,972 of Schmidtke et al. entitled “Multi-Plane Translating Cartridge Handling System”. This patent is hereby incorporated by reference for all that it discloses.
The capacity of a cartridge library may be expanded up to a certain point by filling each of its cartridge storage racks with data cartridges. Often, however, additional storage capacity is needed. Some cartridge libraries, such as the HP Surestore 2/20 series cartridge library (made by Hewlett-Packard Company of Palo Alto, Calif.) holds up to twenty data cartridges. The twenty cartridge capacity is divided among two cartridge storage racks, each of which holds two cartridge magazines, and each magazine of which holds five individual data cartridges. Each of the cartridge storage racks is supported by slides that form the basis of a drawer. To add or remove cartridges from a cartridge library, one of its drawers is opened, a cartridge magazine is added or removed, and the drawer is closed.
Once the capacity of the above-described cartridge library is exceeded, cartridge handling capacity may be increased by stacking additional cartridge library modules on top of the existing module, and then integrating all of the stacked modules to form a single, higher capacity cartridge library. There is a limit, however, to the number of cartridge library modules that may be stacked.